This invention relates to the protection of electronic and other sensitive devices against the damaging effects of ionizing radiation, and more particularly, to a protective-coated housing that protects an enclosed electronic or other device.
The space environment has high levels of ionizing radiation, such as cosmic rays, gamma rays, and hard X-rays. The ionizing radiation of space is largely attenuated by the atmosphere and magnetic field of the earth, and does not have a major effect at the surface of the earth. However, the ionizing radiation of space may degrade the performance of some types of devices that are flown in spacecraft in earth orbit or deep space missions and are exposed to the ionization radiation over extended periods of time. This degradation typically occurs in semiconductor-based devices when the ionizing radiation disrupts the microelectronic structure and/or processes.
Various techniques are known to reduce the damaging effects of the ionizing radiation on electronic devices in space. The electronic devices themselves may be hardened by altering their structures, but in some cases that approach is not feasible because it alters the functionality of the protected electronic device.
In another approach, the electronic devices are shielded against the effects of the ionizing radiation by a physical barrier which absorbs the ionizing radiation before it can reach the electronic device. The physical barrier usually includes a thickness of a protective material that absorbs and attenuates the ionizing radiation. In one form, the physical barrier is a housing that is made of the protective material or is coated with a composite material containing particles of the protective material embedded in an organic binder, see for example U.S. Pat. No. 4,833,334. In another form, the physical barrier is a conformal coating of the protective material embedded in an organic binder that is applied directly to the electronic device, see for example U.S. Pat. No. 6,261,508.
While these approaches are operable to various degrees, in cases they require that the protection be thicker and heavier than would be optimal. Those which construct the housing of the attenuating material require the providing and machining of large pieces of protective material, often an expensive proposition. Those which use an organic binder are subject to degradation of the binder over time and may require complex processing procedures. Care must be taken to choose organic materials that are not subject to excessive outgassing in space, while still being stable and having good adherence to the housing or package.
There is accordingly a need for an improved approach to the protection against ionizing radiation of electronic devices and other structure in a space environment. The present invention fulfills this need, and further provides related advantages.
The present invention provides a technique for protecting against ionizing radiation, a protective structure, and a protected structure. The present approach applies a protective coating overlying a fabricated housing. The protective coating does not contain organic binders or the like which can outgas or degrade over time. The housing is made to the required shape of materials of construction that are known in other situations. The coating is then applied overlying and contacting the housing, using application techniques that are known in other situations and which are relatively inexpensive. The present approach minimizes the weight and thickness of the protective material that must be used to achieve a selected level of protection.
In accordance with the invention, a method comprises the steps of providing a housing, and spraying a protective coating overlying and contacting at least a portion of the housing. The protective coating comprises at least one ionizing radiation protective material selected from the group consisting of a neutron-shielding material, a gamma-ray/X-ray shielding material, and a capture gamma-ray suppression material. Examples of neutron-shielding materials are iron and copper; examples of gamma-ray/X-ray shielding materials are tungsten, hafnium, tantalum, and lead; examples of capture gamma-ray suppression materials are boron and lithium. The spraying is preferably accomplished by plasma spraying the protective coating, most preferably air plasma spraying or vacuum plasma spraying. Multiple layers of different ionizing radiation protective materials may be sprayed to form the protective coating. This technique produces an adherent, coherent coating on many types of materials that may be used in the housing.
The protective coating is typically sprayed to a thickness exceeding about 0.020 inches, preferably from about 0.020 to about 0.200, and most preferably from about 0.030 to about 0.050 inches, to achieve sufficient attenuating effect against the ionizing radiation. Where there are multiple layers of different ionizing radiation protective materials, each layer is typically of the indicated thickness. An important advantage of the present spray approach is that the thickness of the protective coating may be readily selected, and it may be varied spatially in different areas of the housing according to the amount of protection that is required.
The housing is typically made of a material such as a metal, a ceramic, or a nonmetallic composite material. A metal housing, such as an aluminum-alloy housing, is preferred. The sprayed protective coating is preferably applied over substantially all of the housing, but in some cases it may be applied only over portions of the housing.
An electronic or other type of device sensitive to ionizing radiation is normally placed within and enclosed by the housing with its protective coating. This housing, with its protective coating, and the enclosed electronic device are thereafter exposed to a space environment, in a preferred application.
A structure comprises a housing, and a protective coating of an ionizing radiation protective material overlying and contacting at least a portion of the housing. The protective coating has a sprayed microstructure and comprises at least one ionizing radiation protective material selected from the group consisting a neutron-shielding material, a gamma-ray/X-ray shielding material, and a capture gamma-ray suppression material. Other aspects of the invention as discussed herein may be used in conjunction with the structure.
The structure of the present invention achieves good protection against ionizing radiation in a space environment, or against high-energy radiation in other environments as well. The nature and amount of protection are readily controlled by selecting the materials in the protective coating and the thickness of the protective coating to be as required for the expected exposure conditions. The weight of the structure is no greater than necessary, and the cost of fabricating the housing with the protective coating thereon is relatively inexpensive. The sprayed protective coating adheres well to most housing materials, and the organic-free protective coating does not outgas or degrade over time.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.